How te relax and float while sprinting?

[Kay Brannon]

i train for the 100m sprint but i get so tensed up even in training that i seem to be training so hard to keep up with everyone that i just get slower
when i do relax and float along the track - which is very very rarely - it feels amazing and i do feel a lot better and faster
but unfortantley i cannot keep that feeling everytime i train and it is starting to annoy me because i am not getting any faster with it

I also have read about keeping your jaw relaxed and hands relaxed ect. but that is not my problem i have my hands are relatively relaxed and same for my jaw but my shoulders do seem to come high and do get sore shoulders some times

please any suggestions?

Thanks :